"Prepared for: U.S. Environmental Protection Agency"
Includes bibliographical references [p. 32-35]
Wetlands are important landscape features that provide critical ecosystem services. Properly functioning wetlands retain sediment, attenuate floods, recharge groundwater, and cycle nutrients. They are particularly important in the arid West, where only a small fraction of the landscape supports wetlands. Although the passage of the Clean Water Act (CWA) in 1972 initiated federal regulations to protect wetlands, the ambient condition of wetlands continues to be degraded nationwide (National Research Council 2001). Under Section 305 b of the CWA, all waters of the United States (including wetlands) must be monitored and assessed every two years. To understand the condition of wetlands and riparian areas in Montana, the Montana Natural Heritage Program (MTNHP) conducts ecological integrity assessments (EIA) of wetlands and riparian areas in Montana. This report describes the MTNHP pilot project conducted as an initial step in developing a statewide rotating basin assessment and monitoring strategy. The primary objective of the pilot project was to conduct Level 1 2 3 assessments, describe wetland condition, and identify potential anthropogenic stressors in the Milk, Marias, and St. Marys watersheds in Montana. The target population for assessments was palustrine emergent, scrub shrub, and forested wetlands. We used National Wetland Inventory (NWI) polygons mapped from 1980s aerial photography to generate a pool of potential sample sites (i.e., the sample frame) for random site selection. The survey design followed a Generalized Random Tessellation Stratified (GRTS) procedure for discrete objects with reverse hierarchical randomization. This approach accounts for the spatial patterning inherent in ecological systems. We conducted a Level 1 landscape analysis to characterize potential landscape level disturbances at three spatial scales (100 300 and 1 000 meters) around the wetland perimeter. The Level 1 landscape analysis also included landscape profiles using 161 003 NWI palustrine wetland polygons and ancillary data sources to summarize these and other attributes at the fourth, fifth, and sixth code hydrologic unit levels. We performed Level 2 rapid wetland assessments at 123 sites selected for field data collection. Field ecologists used the Montana EIA form to assess wetland condition for all wetland types within the project area. The EIA approach uses a set of ecological attributes that reflect both the structure and function of the wetland to assess ambient condition. Each ecological attribute contains one or more indicators to represent the status or trend of the attribute. These indicators are measured by metrics that include narrative ratings scaled along a gradient of wetland condition status. Each metric consists of three to five narrative statements that are assigned along an ordinal scale value. Higher numbers correspond with increasing levels of disturbance. Each metric rating is summarized into an overall attribute score for five attributes 1) Landscape Context 2) Relative Patch Size 3)Biotic 4) Physicochemical and 5) Hydrology. The ratings for these five attributes are then combine to produce an overall EIA condition score. The MTNHP EIA method uses vegetation as an intensive biological measure to assess wetland condition. Intensive Level 3 vegetation data were collected at 44 of the Level 2 sites using a 20 m x50 m relev plot. Level 3 vegetation data were used to conduct a Floristic Quality Assessment (FQA). The Level 1 landscape analysis showed little variability at all three spatial scales. This is due, in part, to the homogeneity of the landscape within the project area. The dominant land uses in this part of Montana are dry land farming and livestock grazing, and much of the area is intersected by local dirt roads. With so little variability in the landscape, the landscape level analysis did not provide a reliable assessment of wetland condition. Wetland profile results indicated that 81% of the wetlands within the project area are palustrine emergent wetlands with either temporary or seasonal water regimes. Approximately 101, 400 acres of depressional wetlands occur within the project area. Three watersheds had a greater number of altered wetlands than unaltered wetlands Results for the Level 2 rapid assessments indicate that among depressional wetlands, Great Plains Prairie Potholes and Great Plains Saline Depressions are in better condition than either Great Plains Open or Closed Depressions. Results for open and closed depression wetlands indicate that these systems are highly susceptible to human disturbances. Northwestern Great Plains Riparian systems also had more sites ranked as severely altered, suggesting that these systems need more focused protection. Our Level 3 results indicate that most of the wetlands assessed are dominated by species that can tolerate moderate disturbance as demonstrated by the cover-weighted mean c-values ranging from four to six. In addition, lower adjusted FQI values indicate that most of the assessed sites are dominated by plants that are frequently found in disturbed sites. The dominant human disturbances observed and affecting wetland condition in the project area include roads, conversion of temporary and seasonal wetlands to dryland farming and stock ponds, and soil and vegetation disturbance associated with heavy livestock grazing. Effects of human induced disturbance may covary with natural disturbances including drought. Drought may affect wetland condition more than either local or landscape level human disturbances. There are several confounding issues with assessing wetlands in this region. Depressional wetlands are dynamic systems where wet-drought cycles influence the ecological communities present. Therefore, our assessments are just a snapshot of the ecological condition of the wetland at that stage within its wet-drought cycle. Because assessment results may change depending on the wet-drought cycle it is important to assess reference wetlands over a long period of time to establish a gradient of known conditions for wetlands with different water regimes. Both the Level 1 and Level 2 analysis need further calibration and refinement based on intensive Level 3 assessments. Additional Level 3 assessments should be developed to help in the further validation of our methods. Based on this pilot project, the MTNHP will continue to develop indicators and metrics for a long-term integrated, statewide, multijurisdictional wetland condition monitoring and assessment strategy based on EPAs recommended elements
byJones, W. Marc; Montana.Dept. of Environmental Quality; United States.Environmental Protection Agency; Montana Natural Heritage Program; Montana State Library; Montana Natural Resource Information System